Ceramic honeycomb articles are widely used as anti-pollution devices in the exhaust systems of automotive vehicles, both as catalytic converter substrates in automobiles, and as particulate filters in diesel-powered vehicles. Ceramic honeycomb articles for use in such applications are formed from a matrix of thin, porous ceramic walls which define a plurality of parallel, gas conducting channels. In ceramic honeycomb articles used as catalytic substrates in automobiles with gasoline engines, the gas conducting channels are open at both ends. A catalytic coating is applied to the outer surfaces of the walls. Exhaust gasses flowing through the channels come into contact with catalytic coatings on the surfaces of the walls. These honeycomb articles are referred to as flow-through substrates. In diesel systems, exhaust gasses also come into contact with catalytic coatings on the surfaces of the walls. In diesel applications, the ceramic honeycomb articles may also have end-plugs in alternate gas conducting channels to force exhaust gasses to pass through the porous channel walls in order to capture and filter out soot and ash particulates prior to exhaust discharge. These ceramic honeycomb substrates are referred to as ceramic wall-flow particulate filters and, more specifically, as diesel particulate filters.
Application of the catalyst washcoat to the honeycomb substrate alters the properties of the honeycomb structure as the washcoat is deposited on the walls and within the pores of the honeycomb substrate. This results in an increase of backpressure for exhaust gasses flowing through the honeycomb. Furthermore, the extreme temperature fluctuations experienced by honeycomb articles used in both automotive and diesel applications makes the ceramic honeycomb articles susceptible to temperature-induced cracking which leads to the degradation of the honeycomb articles.
Accordingly, a need exists for alternative porous ceramic honeycomb structures with decreased back pressure gain after coating with a catalyst washcoat.